This is the second of a three year proposed study to develop a canine model to determine angiographic, hemodynamic, and pathologic correlates of critical versus non-critical coronary artery narrowings. To this aim, a collaborative effort under the auspices of the Division of Cardiology and the Division of Cardiothoracic Surgery has been formed. Critical lesions both at rest and at high flow states will be defined in terms of reduction of flow and not as an alteration of geometric configuration. Constrictions will be made by surgically placing occluders of known dimensions around a coronary artery. Comparisons are presently being made between the angiographic appearance of these coronary artery constrictions and those observed at post mortem. In addition, those factors that experimentally determine coronary artery bypass graft patency will be investigated. All dogs are followed on a chronic basis to determine long-term graft patency and the effect of collaterals on graft patency. In order to minimize the formation of collaterals, the right coronary artery is presently being utilized. A comparison will be made between the results of this study and an existing in vitro study currently investigating pulsatile flow in artificial compliant arteries.